Sunday, September 20, 2009

Lightweight Battery (1 of 2)

(part one of a two part article)

After years of riding bikes that are complicated and heavy I have become a little bit obsessed with weight, motorcycle weight that is. Generally, having low weight means: better cornering, better braking, better acceleration and easier to ride. Also known as... more fun.

This is why I chose a VUN in the first place. The VUN weighs around 135kg (dry) if fitted with Marvic Mag wheels. This is light, but it could be lighter. I have set a goal to get my VUN down to around 120KG (dry). I'll be documenting each step I take to reach this goal here on this Blog.

Choosing a Lighter Battery

The VUN's standard battery weighs about 3.7KG. How much of that can be saved by using modern lightweight battery technology? I did some research and found a bunch of solutions ranging from regular lead-acid batteries with carbon fiber casing to lithium ION battery packs. Some people recommend just getting a smaller (and thus lighter) lead-acid battery.
  • Carbon fiber cased lead-acid batteries seem like a waste of money. The weight in any lead-acid battery is: 1) the lead and 2) the acid. Paying money to make the plastic casing lighter does not make sense.
  • From what I have read, 'regular' Lithium ION batteries are not suitable. They would require special charging circuits and seem to be unreliable (even potentially hazardous). I would keep away from these.
  • Do not fit a smaller (less powerful) lead-acid battery to your VUN. See below to read why.
Lithium Ferrous Technology

After some research I chose a 4.6 amp hour Speedcell Lithium Ferrous battery. Here are the specs:

- Pulse discharge @ 10 seconds = 240 Amps
- Continuous discharge (MAX) = 140 Amps
- Cycle Life = 1,000 cycles

- Dimensions = 10.5cm (L) x 5cm (W) / 4.13" (L) x 1.96" (W)
- Rating = 4.6Ah
- Weight = 766.57g / 1.69lbs!

Yep, that's 766 grams vs. the standard battery's weight of 3.7KG. A weight saving of 3KG.

Speedcell battery - side view. Very light and small too.

Important: VUN Starting Requirements!

I could have chosen an even lighter Speedcell battery and saved another 300 grams, but this would have compromised the ability to quickly and easily start my VUN. Never fit a less powerful battery to your VUN! The VUN requires a strong battery for no-fuss starting.

A big (650cc) single is hard to start. Singles also have a tendancy to "kick back". This is what happens during starting when the fuel ignites as the piston is still rising up in its compression stroke. If this happens then it can reverse the direction of rotation of your engine for a short period. This is not very good for your starter motor gears.

The VUN electronically retards the ignition timing for 3-seconds during starting. This prevents kick-back. However, if your engine does not start within 3-seconds, then you run the risk of a kick-back and potential damage to the gears that engage your starter motor. This is why you need a strong battery. A strong battery will always start your bike quickly. A battery that is not so strong will not.

The moral of this story: After 3-seconds take your finger off the starter button, no matter what... and if your battery is getting weak, buy a new one.

More About the Speedcell

Unlike a lead-acid battery, claim that the Speedcell will only drain by about 2% when left off charge. This means that you never need to run a trickle-charger to keep it topped up. Its operating temperature is from -50 C to 49 C. Battery life should be at least equal or greater than that of a lead-acid battery (depending on how well you look after your lead-acid battery). The battery is designed to work with your standard charging system.

Lithium Ferrous cells are currently the battery of choice in electric vehicle applications.

Buying the Battery

I bought my battery over the web from Motowheels. Their price is $250, for the 4.6Ah SBK model I chose. This is much more than the cost of a standard battery obviously, but it is pretty good value in terms of $/KG of weight savings. Think about the cost of a carbon fibre seat for your VUN. The seat costs  €803 (plus tax) for a savings of about 1kg.

The Motowheels website was well set up and ordering the battery was easy. The battery arrived after about 2-weeks. It was well packaged and arrived in perfect condition and 100% charged! I guess the "no-loss" claim is true. It also weighed slightly less than advertised: 650 grams against 766 grams so I was happy about that.

What I was not happy about was the shipping costs of $145. This was 60% of the cost of the battery and seems excessive. I knew in advance what the shipping costs were but the Motowheels web site actually said that this would be the "maximum" cost and they would refund any difference between this and the actual cost. Instead, when I checked my credit card, I found that the cost had increased by an additional $35 (total shipping $180), so I feel like I got ripped-off. Maybe this is one of the disadvantages of living in the Czech Republic.

If you are based in Europe then I would try to find a local European source and avoid all this shipping rip-off nonsense. Durbahn, is a German manufacturer and reseller of performance motorcycle parts. They offer a similar product in their English-language web-shop. The 4.6 Amp-Hour model costs €176.31 (including tax) which is almost the same cost as the Speedcell at today's exchange rate. I have never used Durbahn or their products so I can't vouch for them, but it looks like you will get the same product without the high shipping charges if you are based in Europe.

(in part two: fitting and testing the Speedcell battery)

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